boolean slice no longer part of blender 2.8?
It's using the Bool Tool Plugin

The tools belong to the Bool Tool plugin. They do not come with the vanilla B 2.80, you'll have to install a compatible version of the plugin.

You can find it here:
https://gist.github.com/derappelt/603883d70a56c5d1f5080c2980bb5b9f

Then you should look for the Object menu, at the bottom you'll find the BoolTool operators you were looking for: